Digital Cutaneous Branches of Median Nerve

OVERVIEWKey Points:

• Assessing injury to these nerves requires a high index of clinical suspicion based on injury/lacerations and clinical findings. Testing of both the medial/ulnar and lateral/radial aspect of the fingers should be done for finger level lacerations. Failure to repair lacerations often leads to neuroma formation and pain in addition to loss of normal function.

Sensory Innervation:

• Provides sensation to the anterior/volar and lateral/radial cutaneous aspect of the hand including the thumb/index/long and radial half of the ring fingers.• Originates from roots C6, C7 and branches from the median nerve.

EXAMINATIONSensory examination includes testing the following three components innervated by the digital cutaneous branches of the median nerve:

1. Volar and lateral aspect of the hand (except thumb base, where palmar cutaneous branch of median nerve provides sensation).2. Volar thumb/index/long and radial half of the ring fingers.3. Distal dorsal aspect of the thumb/index/long and radial half of the ring fingers.

Sensory Examination:

• Ask patients to draw area of diminished sensation/numbness on a body diagram.• Test the skin along the territories described above for reduced/absent sensation by use of light touch or other sensory examination modalities.• A quick test includes testing the autonomous zone of the median nerve--the index finger volar tip. • The autonomous zone for a single digital nerve is the ulnar or radial side of the digit at the level of the middle phalanx. The distal phalanx level is not an autonomous zone because of overlap from the opposite normal digital nerve. This is especially important for detecting digital nerve injury of the radial or ulnar digital nerve to the affected finger but not both.

Clinical Relevance:

• Provides sensation to the territories described above.• Patients exhibiting symptoms of carpal tunnel syndrome or median nerve compressions proximally will include reduced sensation along this sensory territory. • The median nerve branches into sensory nerves that innervate the described territory, which includes the 1st, 2nd, and 3rd webspace. Injury to any of these branches can occur and produce sensory loss to their corresponding territories. It is critical in understanding the median sensory nerve anatomy within the hand when examining this nerve.• See above regarding the specific autonomous zone exam to detect individual radial or ulnar digital nerve injuries due to trauma to the fingers.

Course: Branches of the digital cutaneous nerves include the common and proper digital cutaneous branches. The median nerve branches into four sensory nerves within the hand and are composed of the following orientation: common, proper, common, and common (lateral to medial, anteriorly). The most lateral/radial common branch innervates the volar aspect of the thumb. The proper branch innervates the lateral/radial side of the index finger. The middle common branch innervates the 2nd webspace (and goes to the medial/ulnar index finger and lateral/radial long finger). The most medial common branch innervates the 3rd webspace (and goes to the medial/ulnar long finger and the lateral/radial ring finger).

Communicating Branch from the Ulnar Nerve: There exists a communicating branch that originates from the ulnar nerve. This branch originates from the digital cutaneous branch of the ulnar nerve that innervates the medial/ulnar aspect of the ring finger. The branch then combines with the proper digital cutaneous branch of the median nerve that innervates the lateral/radial aspect of the ring finger. This variation occurs in (46%) of cases. A second variation exists where the communicating branch combines with two proper digital cutaneous branches of the median nerve innervating the 3rd webspace. This variation occurs in (20%) of cases. The third variation is that no communicating branch between the median and ulnar nerve exists. This occurs in the other (20%) of cases. This communicating branch is often referenced as the Berretini anastomosis for the ulnar and median nerve anastomosis in the palm.